This adds functionality so that on `rad sync` and `rad clone`, we
connect to known seeds if necessary, before attempting to fetch.
In passing, some related changes were made:
* The `rad sync` command's arguments were reworked:
`--replicas <count>` can be used to specify a replica count when
fetching
* The `rad patch` command no longer has a `--fetch` option
* It's now possible to tell the node not to automatically connect to
peers in the background
* `AddressBook` is being used underneath `Seeds` to allow for shuffled
iteration
This command announces refs to peers and waits for them to be
in sync.
Adds a subscribe method to `Handle` so that we can get the events
from the seed to allow us to confirm that the configured seeds fetched
from us.
cloudhead
Alexis Sellier